1. Field of the Invention
The present invention relates to video recordation and, more particularly, to advantageous methods and system arrangements and apparatus for object selective video recording in automated screening systems, general video-monitored security systems and other systems, in which relatively large amounts of video might need to be recorded.
2. Known Art
Current state of the art for recording video in security and other systems is full time digital video recording to hard disk, i.e., to magnetic media as in the form of disk drives. In some systems digitized video is saved to magnetic tape for longer term storage.
A basic problem of digital video recording systems is trade-off between storage space and quality of images of stored video. An uncompressed video stream in full color, VGA resolution, and real time frame rate, may require, for example, about 93 Gigabytes (GB) of storage per hour of video. (Thus, 3 bytes/pixel*640 pixels/row/frame*480 pixels/column/frame*30 frames/sec*60 sec/min*60 min/hr.)
A typical requirement is for several days of video on PC hard disk of capacity smaller than 93 GB. To conserve disk space, spatial resolution can be reduced, frame rate can be reduced and compression can be used (such as JPEG or wavelet). Reduction of spatial resolution decreases storage as the square root of the reduction. I.e., reducing the frame size from 640×480 by a factor of 2 to 320×240 decreases required storage by a factor of 4.
Reduction of frame rate decreases storage linearly with the reduction. I.e., reducing frame rate from 30 FPS (frames per second) to 5 FPS decreases storage by a factor of 6. As frame rate decreases video appears to be “jerky.”
Reduction of storage by compression causes a loss of resolution at higher compression levels. E.g., reduction by a factor of 20 using JPEG format results in blurred but may provide usable images for certain purposes, as herein disclosed.
Different methods of storage reduction discussed above are multiplicative in affect. Using the reductions of the three examples above reduces storage requirements by a factor of 480
(4*6*20) to 193 MB/hour.
Also known is use of video motion detection to save only frames with any motion in the video. The cause of the motion is not analyzed. Thus, each full frame must be stored at the preset compression. The effect of motion detection on storage requirements is dependent on the activity in the video. If there is any motion half of the time, storage requirement is reduced by a factor of two.
In the current start of the art, some attempts have been made to improve the efficiency of video recording by increasing the resolution during a period of interest.
Some time lapse VCRs have used alarm contact inputs from external systems that can cause the recording to speed up to capture more frames when some event of interest is in a camera view. As long as the external system holds the alarm contact closed the recording is performed at a higher rate; yet, because the contact input cannot specify which object is of interest the entire image is recorded at a higher temporal resolution (more frames per second) for the period of contact closure. This can be considered to be period selective recording.
Some digital video recording systems have included motion detection that is sensitive to changes in pixel intensity in the video. The pixel changes are interpreted simply as motion in the frame. In such a system, pixels are not aggregated into objects for analysis or tracking. Because accordingly there is no analysis of the object or detection of any symbolically named event, the entire image is recorded at a higher temporal resolution while the motion persists. This can be considered as motion selective recording.
The recently announced MPEG-4 Standard uses Object Oriented Compression to vary the compression rate for “objects”, but the objects are defined simply by changes in pixel values. Headlights on pavement would be seen as an object under MPEG-4 and compressed the same as a fallen person. Object selective recording in accordance with the present invention is distinguished from MPEG-4 Object Oriented Compression by the analysis of the moving pixels to aggregate into a type of object known to the system, and further by the frame to frame recognition of objects that allows tracking and analysis of behavior to adjust the compression rate.
The foregoing known techniques fail to achieve storage requirement reduction provided by the present invention.